<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1,maximum-scale=1,user-scalable=no" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <button>页面一</button>
    <select id="are">
    	<option value="">全部</option>
    </select>
    <button class="btn1">让北京选中</button>
</body>
<script src="./js/jquery-1.8.3.min.js"></script>
<script>
	$(".btn1").click(function(){
    	$("#are").val(2);
    })
	var a = 1;
	var str = "";
	var arr = ["河北","天津","北京","河南","山东"]
	for(var i=0;i<5;i++){
		
		if(i == a){
			str += "<option selected value='"+i+"'>"+arr[i]+"</option>";
		}else{
			str += "<option value='"+i+"'>"+arr[i]+"</option>";
		}
		
	}
	$("#are").append(str);
    

</script>
</html>